The invention relates generally to communications over a communications network and more particularly to systems and methods for delineating a cell in the communications network.
The communications networks transport information among a number of locations. The information is usually presented to the communications network in the form of time domain multiplexed electrical signals, time domain multiplexed optical signals, or a combination of electrical and optical signals, and represents any combination of voice, video, and computer data. The communications networks include various physical sites interconnected by links.
DS1 is one type of electrical digital communications link. A DS1 link is capable of carrying 24 channels which are time domain multiplexed (TDM) and transmitted over a physical line. A DS1 link transmits one DS1 frame 8000 times per second or one frame every 125 microseconds. Each DS1 frame includes a DS1 payload with 24 timeslots, one for each channel with 8 bits in each timeslot. Each DS1 frame also has a DS1 overhead bit. One type of the overhead bit is a frame bit that identifies the start of the DS1 frame. An example of payloads mapped within the DS1 frames is asynchronous transfer mode (ATM) cells.
A DS1 extended superframe (ESF) is a group of 24 DS1 frames. Each ESF superframe includes an ESF overhead bit section that has 24 overhead bits, and an ESF payload section that has 24 samples of each of the 24 channels.
When the DS1 frames are in ESF format, layers of synchronization are used to find the DS1 frame #1 of the 24 DS1 frames in an ESF superframe. In other words, an ESF framer determines the location of the DS1 frame bits so that successive DS1 frames can be distinguished. The ESF framer also determines DS1 frame #1 in an ESF superframe so that successive ESF superframes can be distinguished. After the ESF framer locates the ESF superframes, cell delineation hardware locates the ATM cells in DS1 links that have an ATM payload to enable the monitoring or manipulation of the ATM cells.
DS1 framing is used whenever synchronization is lost. However, in conventional communications networks, complicated hardware is used to perform DS1 framing. Moreover, the hardware used to perform DS1 framing today is not scalable to an adequate extent. Additionally, it takes conventional framing and the cell delineation hardware a long time to distinguish one DS1 frame from another and find ATM cells within the DS1 frames.